1 00:00:05,680 --> 00:00:07,678 Hi, welcome to this new video. 2 00:00:07,678 --> 00:00:12,100 We're going to continue working on project 1, which is a particle system, and 3 00:00:12,100 --> 00:00:14,046 we're going to be adding forces. 4 00:00:14,046 --> 00:00:19,190 So let's talk a little bit about forces that we can apply to a particle, right? 5 00:00:19,190 --> 00:00:25,057 So it will happen that we might want to control a particle in some particular way, 6 00:00:25,057 --> 00:00:30,487 and we will do that by including certain forces, forces such as gravity, 7 00:00:30,487 --> 00:00:34,186 wind, turbulence, drag and so forth, right. 8 00:00:34,186 --> 00:00:38,744 So these forces are external influences that make the particles change, and 9 00:00:38,744 --> 00:00:42,234 they're mostly represented as form of vectors, right. 10 00:00:42,234 --> 00:00:46,474 So the vectors will, in some cases, might have a position, right. 11 00:00:46,474 --> 00:00:51,244 If you think of a fan, like it might have a position, but in other cases, 12 00:00:51,244 --> 00:00:54,295 it would be just something like gravity that is 13 00:00:54,295 --> 00:00:59,514 basically applying a force that is a downward force at all times, right. 14 00:00:59,514 --> 00:01:04,154 So, let's just evaluate how we would actually do the computation of forces. 15 00:01:04,154 --> 00:01:08,798 In order to do kind of a physics based computation of forces, we're going to use 16 00:01:08,798 --> 00:01:13,786 three variables, we've been using two so far, which is position and velocity. 17 00:01:13,786 --> 00:01:17,566 And this is a simple way of updating the position of a particle, but 18 00:01:17,566 --> 00:01:19,556 we're going to add acceleration. 19 00:01:19,556 --> 00:01:22,822 And acceleration, if you really go into what acceleration is, 20 00:01:22,822 --> 00:01:24,652 is the rate of change of velocity. 21 00:01:24,652 --> 00:01:28,212 So velocity is the rate of change of position, right. 22 00:01:28,212 --> 00:01:32,385 So think of the particle is at any time is moving with its velocity, but 23 00:01:32,385 --> 00:01:34,716 that velocity might change, right. 24 00:01:34,716 --> 00:01:37,154 It starts like, maybe like you start getting drag and 25 00:01:37,154 --> 00:01:39,468 that velocity starts getting slower, right. 26 00:01:39,468 --> 00:01:41,423 Or you get a gust of wind and you start, 27 00:01:41,423 --> 00:01:44,484 the velocity starts getting stronger, right. 28 00:01:44,484 --> 00:01:49,634 The way in which velocity changes is affected by the acceleration and 29 00:01:49,634 --> 00:01:55,164 the velocity, in turn, passes, updates the position, right. 30 00:01:55,164 --> 00:01:57,716 So how do we do that in code? 31 00:01:57,716 --> 00:01:59,712 Well, we will need a velocity, sorry, 32 00:01:59,712 --> 00:02:02,468 an acceleration variable that will also be a vector. 33 00:02:02,468 --> 00:02:05,588 A vector that we will refresh every frame, right. 34 00:02:05,588 --> 00:02:09,844 We're going to be recalculating that velocity vector every frame. 35 00:02:09,844 --> 00:02:13,822 But the velocity vector won't be refreshed every time, every turn, right. 36 00:02:13,822 --> 00:02:17,248 We're going to keep that velocity vector what it is, and 37 00:02:17,248 --> 00:02:22,774 either the acceleration will subtract or add to that velocity, right. 38 00:02:22,774 --> 00:02:27,641 The important thing is that we do this sequence of, we pass the acceleration, 39 00:02:27,641 --> 00:02:32,494 it's added to the velocity, the velocity is added to the position, right. 40 00:02:32,494 --> 00:02:34,382 And then we reset the acceleration. 41 00:02:34,382 --> 00:02:38,450 Those are the third, the first three lines of the update particle and 42 00:02:38,450 --> 00:02:43,076 then when we compute forces, we do any force over the acceleration, right. 43 00:02:43,076 --> 00:02:48,658 So we might encounter we're close to a proximity of, again, like a fan, 44 00:02:48,658 --> 00:02:53,521 and the particle might start flying in a particular direction, 45 00:02:53,521 --> 00:02:58,356 or we just basically add gravity to the acceleration, right. 46 00:02:58,356 --> 00:02:59,540 Or something like that. 47 00:02:59,540 --> 00:03:03,910 So let's see how that kind of plays out when we start adding this 48 00:03:03,910 --> 00:03:05,908 information to our code. 49 00:03:05,908 --> 00:03:08,424 Let's jump into our script. 50 00:03:10,044 --> 00:03:14,684 So I'm here back at our script where we left it from last video, 51 00:03:14,684 --> 00:03:18,764 if you haven't covered that video, start there. 52 00:03:18,764 --> 00:03:23,224 So this is the second video in the project 1 series. 53 00:03:24,564 --> 00:03:28,554 So let's see, we're going to be doing most of our work, I mean, just as a recap, 54 00:03:28,554 --> 00:03:29,652 where we should be. 55 00:03:29,652 --> 00:03:32,241 It's like we have an emitter, right, 56 00:03:32,241 --> 00:03:35,384 spreading particles from the center, right. 57 00:03:36,394 --> 00:03:41,444 And if we go into our particle tab, we will see that our 58 00:03:41,444 --> 00:03:47,396 update calculation at the moment is rather straightforward, 59 00:03:47,396 --> 00:03:51,154 it uses self position.addvelocity. 60 00:03:51,154 --> 00:03:54,554 So to the position we add the velocity. 61 00:03:54,554 --> 00:03:58,923 We need to do an extra step here, so 62 00:03:58,923 --> 00:04:02,388 we need to add a new vector, 63 00:04:02,388 --> 00:04:07,684 self.acceleration, so let's do ack. 64 00:04:10,544 --> 00:04:16,464 So this is going to be a new Pvector, 0,0, so it's going to be empty. 65 00:04:16,464 --> 00:04:20,404 So we're going to allow forces to interact with this vector. 66 00:04:21,424 --> 00:04:24,717 And now in the update, we're going to say, 67 00:04:24,717 --> 00:04:29,474 let's just add the acceleration to the velocity, right? 68 00:04:29,474 --> 00:04:33,927 So self.velocity.add 69 00:04:33,927 --> 00:04:40,234 self.acceleration, right? 70 00:04:40,234 --> 00:04:43,914 Right now the acceleration is zero, so there shouldn't be any difference, right. 71 00:04:43,914 --> 00:04:49,272 We should be able to run this and nothing should change, 72 00:04:49,272 --> 00:04:54,046 but we want to start changing this acceleration. 73 00:04:54,046 --> 00:04:59,179 The other thing that I want to do, as I mentioned before, 74 00:04:59,179 --> 00:05:04,640 we want to reset the acceleration at the end of every frame, 75 00:05:04,640 --> 00:05:09,994 every update, basically we calculate the new position, 76 00:05:09,994 --> 00:05:14,006 but then also we reset the acceleration. 77 00:05:14,006 --> 00:05:19,454 So the acceleration goes back to zero after the update function, right. 78 00:05:19,454 --> 00:05:24,086 So what we're going to do is include a new function and again, 79 00:05:24,086 --> 00:05:28,811 remember that we're kind of trying to be modular in terms of, 80 00:05:28,811 --> 00:05:32,854 how we write our code and so that we can maintain it. 81 00:05:32,854 --> 00:05:36,220 And often if we find mistakes, 82 00:05:36,220 --> 00:05:41,140 it will be just within one little chunk of it, 83 00:05:41,140 --> 00:05:45,034 compute_forces, self, right. 84 00:05:46,194 --> 00:05:52,734 Here, what we're going to do is add, so in the compute forces function, 85 00:05:52,734 --> 00:05:58,146 we're going to add one force to the acceleration, right? 86 00:05:58,146 --> 00:06:05,362 So let's create a force here, we could say g for gravity, right? 87 00:06:05,362 --> 00:06:07,734 Or we could even call it gravity. 88 00:06:08,954 --> 00:06:15,210 It would be a Pvector 89 00:06:15,210 --> 00:06:23,766 of 0,0.01, right. 90 00:06:23,766 --> 00:06:27,571 So I want to just give it a very small push, remember that this is something that 91 00:06:27,571 --> 00:06:30,566 is going to be affecting the velocity every frame, right? 92 00:06:30,566 --> 00:06:33,454 So we're going to put a very small number here, 93 00:06:33,454 --> 00:06:37,006 it's going to be our kind of synthetic gravity, right. 94 00:06:37,006 --> 00:06:40,592 Something that would represent a form of like a downward motion, 95 00:06:40,592 --> 00:06:43,282 we know in processing that the y-axis is down. 96 00:06:43,282 --> 00:06:46,431 So we're going to be assuming that the particles will have gravity falling down, 97 00:06:46,431 --> 00:06:49,534 but you could actually create an arbitrary gravity in any direction, right. 98 00:06:51,514 --> 00:06:58,357 So that's the gravity vector or yeah, the gravity vector going down and 99 00:06:58,357 --> 00:07:04,654 let's just add that self.acceleration.add gravity, right. 100 00:07:08,454 --> 00:07:12,411 So this is kind of, we're using these compute forces here, 101 00:07:12,411 --> 00:07:14,606 this is kind of a global force. 102 00:07:14,606 --> 00:07:18,316 Later, we're going to see how to create forces that it's a class and 103 00:07:18,316 --> 00:07:21,414 it can interact with our particles in different ways. 104 00:07:21,414 --> 00:07:25,978 But right now we're just creating kind of a general understanding of how forces 105 00:07:25,978 --> 00:07:28,034 would be computed into the system. 106 00:07:29,294 --> 00:07:32,254 So we have that, so we have compute forces. 107 00:07:32,254 --> 00:07:36,500 The last thing we need is actually to invoke this line of code. 108 00:07:36,500 --> 00:07:42,010 So our function computeforces self.com put forces here, 109 00:07:42,010 --> 00:07:45,044 we'll do it at the beginning. 110 00:07:45,044 --> 00:07:48,100 So before the update, it needs to be done before the update. 111 00:07:48,100 --> 00:07:53,329 If you remember any, the update will actually delete or 112 00:07:53,329 --> 00:07:57,860 make sure that the acceleration is zero here. 113 00:07:57,860 --> 00:07:59,628 So let's see what we get at this point. 114 00:07:59,628 --> 00:08:04,929 Let's see, so we have, you see the same particles now go out, 115 00:08:04,929 --> 00:08:10,784 but they actually fall and they actually fall based on this gravity. 116 00:08:10,784 --> 00:08:14,769 If you want this gravity to be stronger, 117 00:08:14,769 --> 00:08:20,171 you could see that the particles fall weaker, right. 118 00:08:20,171 --> 00:08:25,891 So that's kind of neat, we could actually start including, 119 00:08:25,891 --> 00:08:32,844 as I said, we could actually include that 0.502 in the x-axis. 120 00:08:32,844 --> 00:08:38,284 And you would see that you can create a force in this direction, right. 121 00:08:38,284 --> 00:08:42,196 And because we're starting the particles with a velocity that is random, right. 122 00:08:42,196 --> 00:08:47,128 Some of them will start in an upward direction, downwards, left and 123 00:08:47,128 --> 00:08:50,756 right, so you get this kind of explosion effect. 124 00:08:50,756 --> 00:08:54,414 But if you want to manipulate the initial velocity, 125 00:08:54,414 --> 00:08:57,634 you would go back to the this definition. 126 00:08:57,634 --> 00:09:00,906 How is the initial velocity being defined? 127 00:09:00,906 --> 00:09:03,930 If you don't want to see any difference in the particles, 128 00:09:03,930 --> 00:09:07,242 you might just put a zero there and the velocity to start with. 129 00:09:07,242 --> 00:09:12,356 And you will depend primarily on the acceleration provided by the force, 130 00:09:12,356 --> 00:09:15,954 that's something that you can also try. 131 00:09:15,954 --> 00:09:18,645 But at this point, we have a good setup, 132 00:09:18,645 --> 00:09:23,076 we know how to apply forces to our particles, so we can really start 133 00:09:23,076 --> 00:09:28,354 tinkering on how to create a system that is more expressive and more complex. 134 00:09:28,354 --> 00:09:29,304 So I'll see you in the next video.